Structural effects of electrochemical oxidation of formic acid on single crystal electrodes of palladium.

Structural effects on the rates of formic acid oxidation have been studied on Pd(111), Pd(100), Pd(110), and Pd(S)-[n(100)×(111)] (n = 2−9) electrodes in 0.1 M HClO4 containing 0.1 M formic acid with use of voltammetry. On the low index planes of Pd, the maximum current density of formic acid oxidation (jP) increases in the positive scan as follows:  Pd(110) < Pd(111) < Pd(100). This order differs from that on the low index planes of Pt:  Pt(111) < Pt(100) < Pt(110). Pd(S)-[n(100)×(111)] electrodes with terrace atomic rows n ≥ 3 have almost the same jP as Pd(100), except Pd(911) n = 5. The value of jP on Pd(911) n = 5 is 20% higher than those of the other surfaces. Pd(311) n = 2, of which the first layer is composed of only step atoms, has the lowest jP in the Pd(S)-[n(100)×(111)] series. The adsorption geometry of the reaction intermediate (formate ion) is optimized by using density functional theory.